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Some fabrics are more effective than others for making DIY face masks — here’s which ones are best

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It’s official — the U.S. Centers for Disease Control and Prevention recommends that all Americans wear a face cloth covering in public settings.

To preserve the supply of N95 and surgical masks for health care workers treating patients who have contracted COVID-19, the disease caused by coronavirus, the CDC has advised all Americans to instead wear “cloth face coverings in public settings where other social distancing measures are difficult to maintain.” Examples include grocery stores and pharmacies, the CDC says.

But some of the materials you can use to make do-it-yourself face masks offer more protection than others.

Widespread mask usage can help reduce asymptomatic transmission of COVID-19

The CDC’s recommendation comes following numerous reports on transmission of COVID-19 from asymptomatic people.

These people don’t have fevers, coughs or runny noses or other common symptoms of COVID-19, and may be unknowingly spreading the virus to others, according to one study which examined infections of residents of a nursing home in King County, Washington .

Because seemingly healthy people could end up infecting someone, public health officials are now recommending that all Americans wear a face covering in public

Which materials work best?

Following President Donald Trump’s announcement on Friday regarding face masks, Jerome Adams, U.S. Surgeon General shared a video on Twitter TWTR, +7.96% explaining how to make your own mask.

He suggested using items you could find around the house like “an old scarf, a bandanna or a hand towel… or an old T-shirt,” to make a mask.

For instance, tea towels are better to use for a mask than T-shirts or pillowcases, according to research published by the Stanford Anesthesia Informatics and Media Lab.

Another recent study showed that different types of cloth offer significantly different levels of protection.

“Some cotton fabrics filter less than 25% of air particles,” said Dr. Scott Segal, chairman of anesthesiology at Wake Forest Baptist Health, a North Carolina medical center, who launched a research project to study the effectiveness of materials used to make homemade masks.

Of the 13 different homemade cloth surgical masks Segal studied in partnership with the Wake Forest Institute for Regenerative Medicine, “quilters’ cotton” ranked highest.

The study used instruments that detected a fabric’s effectiveness at filtering small particles. Quilters’ cotton, a tightly woven high-thread-count fabric, can filter out some 70-79% of small particles including viruses, according to Segal’s research, which has not been submitted for publication and has not been peer-reviewed. That’s better than surgical masks, which Segal said filter out only 65% of particles. (N95 masks offer the highest level of protection — filtering out 95% of air particles.)

Segal’s team has not yet tested cotton bed sheets, which one epidemiologist recommended for crafting a DIY mask, or balaclavas (face coverings similar to ski masks) which are typically made from materials similar to what’s used in activewear.

One way to find out on your own if a material is a good candidate for a mask is to do what Segal refers to as “the light test.” Take the material and “hold it up to a bright light,” Segal said. “If you see light between fibers it’s not a good filter. Even on dark fabrics if you hold them up to light or to the sun you will still be able to see if the fabric’s fibers will show or not.”

After a material passes the light test, the next factor to keep in mind is the fabric’s breathability. One way to test that out, Segal recommended, is to “hold up the material up to your nose and mouth and say ‘If this was tightly adhered to my face would I be able to make it through a trip to the supermarket?’”

Vacuum cleaner bags ranked higher than tea towels but they’re considerably more difficult to breathe through, the Stanford research showed.

If you’re unable to find a material in your home that passes the light test, you shouldn’t give up on making a mask. “Anything is better than nothing,” Segal said. In other words, it would be better to go to the supermarket wearing a mask made from a T-shirt as opposed to not wearing any face covering.

Segal and his research team tested a thick “jersey” cotton similar to what’s used for “stretchy shirt” and it performed well, he said. The team plans to test out more common “household” fabrics in the next round, but obtaining more material to test could take a while because “the fabric stores aren’t open much now,” Segal noted.

A mask isn’t a substitute for social distancing

“No mask is as good as social distancing,” Segal said. “I’m worried that once people start wearing masks they might relax social distancing.”

Deborah Birx, a public health expert on the White House’s coronavirus response team, expressed similar concerns during a briefing last week.

“The most important thing is the social distancing and washing your hands, and we don’t want people to get an artificial sense of protection because they’re behind a mask.”